1. Field of the Invention
The invention relates in general to a timing recovery apparatus and an associated method, and more particularly, to a timing recovery apparatus and an associated method to recover timing by gain adjustment.
2. Description of the Related Art
In a communication system, a sampling frequency offset (SFO) is generated at a receiver when sampling rates are mismatched between a transmitter and a receiver. Errors in sampling points will be caused if the sampling frequency offset is left uncompensated. Further, the error may continue to accumulate over time and lead to a severe effect on system performance. Thus, a typical communication system is provided with a timing recovery apparatus for compensating the sampling frequency offset. The timing recovery apparatus may have a data-aided design or a non-data-aided design (otherwise referred to as a blind design). The data-aid design synchronizes the timing of a transmitter and a receiver by utilizing a known pilot signal or training sequence. The synchronization speed established on such design is fast yet occupies additional transmission bandwidth. In contrast, as the non-data-aided design is capable of synchronizing the timing of the transmitter and the receiver without involving the pilot signal or training sequence, no additional transmission bandwidth is consumed. However, this requires a longer period to achieve synchronization. Thus, a system that demands higher standards for synchronization time (e.g., a wireless local area network (WLAN) communication system) usually establishes synchronization by the data-aided design; a system that demands lower standards for synchronization time (e.g., a radio broadcast communication system) usually establishes synchronization by a non-data-aided design.
The timing recovery technology may be further improved although it has been available for a considerable period of time. With the prevalence of mobile devices, frequent relative movements are present between a transmitter and a receiver. The relative movements cause changes in transmission paths and distances to generate a shift in the frequency of a signal received by the receiver. Such occurrence is referred to a Doppler effect, which becomes more noticeable as the speed of the relative movements becomes faster. At this point, the conventional timing recovery technology is insufficient for maintaining stable sampling points, such that a bit error rate or packet error rate of the communications system rises.